The present invention relates to pressure operated shut-off valves of the type controlled by opening of a pilot valve having a flow passage substantially smaller than the main valve for initiating flow without hammering in the flow passages. Valves of this type are known in the art as, for example, those described in U.S. Pat. Nos. 3,593,956 to W. R. McCarty, Jr., 3,593,957 to P. A. Dolter et al., and 3,672,627 to W. R. McCarty, Jr., et al. In the construction of a known pilot control shut-off valve, a main valve member is seated on a valve seat intermediate the valve inlet and outlet. The main valve member is attached to a pressure-responsive diaphragm which divides the inlet side of the valve into two chambers which are interconnected by a bleed passage to the diaphragm. When the main valve is closed, the pressure from the inlet is equalized in the two chambers. A pilot passage is provided through the main valve member and is sealed by a pilot valve normally closed. An electromagnetic actuator, upon energization, opens the pilot valve to permit flow from one of the fluid chambers through the pilot passage to the outlet of the valve. The discharge from the downstream one of the chambers and through the pilot passage to the valve outlet creates a pressure differential across the diaphragm which subsequently opens the main valve member. As the main valve member moves in response to the pressure forces, the main valve member encounters the pilot valve member if the pilot valve has not been moved a sufficient distance from the pilot seat on the main valve against which the pilot is seated in its closed position.
In providing an electromagnetic actuator for moving the pilot valve, previous valve designs have employed an armature chamber fluidically connected to one of the chambers formed by the diaphragm, with the pilot valve contained therein. An armature is disposed within the pilot valve chamber and connected to the pilot valve such that movement of the armature opens the pilot valve. Pole pieces are disposed about the sealed chamber such that the air gap between the end of the pole piece and the armature defines the null or maximum force position of the armature in its movement. A coil is disposed about the pole piece and, upon energization of the coil, the armature moves to the null position and opens the pilot valve by an amount of the armature stroke. In this type of actuator arrangement the armature is required to have a substantial movement in order to position the pilot valve in the open position such that movement of the main valve by pressure forces on the diaphragm will not cause the pilot valve to close, resulting in shutting of the main valve.
When the air gap is made sufficently large in order to provide the required armature stroke for moving the pilot valve the desired distance from its seat, a large magnetomotive force is required from the current flow in the coil in order to cause movement of the armature. The requirement for the relatively long armature stroke and high magnetomotive force has resulted in the need for a substantial number of turns in the coil for a given electrical source or greater electrical power for a given number of coil turns, and thus has resulted in limiting attempts to reduce the size and power requirements of the actuator coil.